The invention relates to a method for controlling the synchronization of cylinder/piston units for counterforce rams and/or vee rings and for reducing pressure peaks during the fineblanking and/or forming of workpieces on a fineblanking or stamping press equipped with at least one tool, in which the cylinder/piston unit is subjected to the control pressure of a hydraulic fluid and the press ram is driven mechanically or hydraulically.
The invention further relates to a device for controlling a piston/cylinder unit for the counterforce ram and vee ring and for reducing pressure peaks during the fineblanking of workpieces for implementation of the method with a fineblanking or stamping press, which is equipped with at least one tool consisting of an upper section and a lower section, which is allocated at least one piston/cylinder unit of the press for at least one counterforce ram and/or vee ring of the tool in addition to one press ram, and with a hydraulic system connected to the piston/cylinder unit, which comprises an accumulator for the storage of hydraulic fluid, hydraulic lines for the inlet and outlet of the hydraulic fluid to and from the piston/cylinder unit, controllable actuators for opening and closing the hydraulic lines and a control unit for activation of the actuators, whereby the press ram is either incorporated in the hydraulic system or connected to a separate drive system.
Fineblanking presses are known to be characterized in that the counterforce ram and the vee ring function as controlled axes and reach their limits in terms of process technology when operating at high cycle rates and fast speeds. The greater the cycle rates and speeds, the faster the pressure relief for the highly pressurized cylinder/piston units needs to be, also resulting in increasing impairment of the synchronization between the main ram of the press and the counterforce ram and vee ring cylinder due to the quantitative dependence of the pressure relief process (DE 2148618A1).
Pressure peaks are likewise known to occur during stamping or blanking on presses. Pressure surges can be observed for example with the so-called cutting shock, which occurs whenever the punch exits the workpiece and the resistance of the material is suddenly absent, or during the impact between the punch and the workpiece clamped between the upper section and lower section of the tool.
Numerous different solutions are known from the prior art, all attempting to reduce the cutting shock through dampening (DE 1 427 403 A, DE 26 21 726 A1, DE 28 12 973 A1, DE 31 12 393 C2, DE 41 25 992 A1).
DE 1 427 403 A1 describes a counterpressure system in a press designed to dampen the cutting shock, in particular in a hydraulic press, which consists of a counterpressure chamber filled with hydraulic fluid in at least one working unit consisting of a piston and cylinder in addition to at least one allocated exit restrictor.
Although this prior art is known to dampen the pressure surge of the cutting shock by means of the counterpressure system and discharge of the pressure pulse into a tank via the point of restriction, it is unable to pick up the pressure surge, which may attain values twice those of the force set during the impact between the punch and the workpiece. This subjects parts to undesirable deformation, quality impairment and increased tool wear.
DE 26 21 726 A1 describes a device designed to prevent cutting shock occurring on blanking presses with at least one cylinder/piston unit, which is positioned between a tool base plate and a press ram with an adjustable height level of a contact surface for the press ram, whereby the stroke of the piston is on the one hand limited by a collar provided on the cylinder and on the other, by the inner face wall of the cylinder facing the face of the piston, and whereby the pressurized medium chamber between the face of the piston and the face wall of the cylinder is connected in the inlet direction to a high-pressure pressurized medium source via a check valve and a pressure relief valve is connected in the outlet direction. The pressure relief valve is provided with a control chamber, which is connected to the high-pressure pressurized medium source, whereby the pressure in the control chamber can be adjusted via a control line by means of a central pressure control valve.
This prior art is likewise known to be unsuitable for reducing or preventing the pressure surge occurring during the impact between the punch and the workpiece, with the result that the disadvantages described above likewise apply to this known solution.
All these known solutions to reduce pressure peaks do not operate independently of quantity, thus not only resulting in speed differentials but also in pressure differentials in the cylinder chambers of the cylinder/piston units depending on the oil temperature.
DE 23 60 821 A1 describes a synchronization control system for hydraulic presses with a plurality of press pistons and a driver located between the high-pressure fluid source and the pressure chambers of the press pistons. The primary side of the driver, the working chamber, is supplied with a constant flow of the uncontrolled working fluid at a preset press piston operating speed and is actuated with a controlled cut-off valve.
This known solution is above all used for forging machines but cannot be applied to fineblanking.